The present invention relates to a power transmission device for vehicles, which transmits a rotaion of a vehicle engine to vehicle driving wheels through an endless belt type infinite variable transmission which uses a clutch unit and hydraulic pressure-controlled speed variable pulleys.
A conventional power transmission device for vehicles with engines including automobiles comprises a magnetic clutch coupled to an engine crank shaft, an infinite variable transmission of a speed variable pulley type coupled to the magnetic clutch and having an endless steel belt, and a gearing for coupling the infinite variable transmission to the driving wheels.
In the conventional power transmission device of this type, a hydraulic device is arranged at a side of one of a pair of drive sheaves for a drive pulley to make them to approach or separate from each other and another hydraulic device is prepared at a side of one of a pair of driven sheaves for a driven pulley to make them approach or separate from each other. A V belt passes through the V-shaped grooves defined between the driving sheaves and between the driven sheaves. The hydraulic device adjusts the groove width of each pulley in accordance with the hydraulic pressure produced in the hydraulic device. With this adjustment, the diameter of a belt wound about the drive and driven pulleys is varied to achieve infinite variable transmission. A hydraulic pump is required to drive the hydraulic devices. The hydraulic pump may be driven by an electric motor. However, in this case, an electric motor must be incorporated in addition to the hydraulic pump, which will increase the cost and volume of the power transmission device. In order to avoid this, the hydraulic pump is driven by power from the engine. In order to always drive the hydraulic pump by power from the engine, the power from the engine is supplied from a rotating part (that is, rotary part at the engine side) between the clutch and the engine. A gearing and a combination of pulleys and a belt are generally used as an intermediate means for transmitting power from the engine. However, they also increase the cost of the device and render the device bulky due to the increased space required. The use of the intermediate means tends to cause power loss.